The rapidly developing field of charge coupled devices and imaging systems has been troubled from the beginning by the non-linear relationship between voltage and charge in semiconductor junctions. It is well known that the capacitance of semiconductive junctions varies approximately as a function of the reciprocal of the square root of the voltage across the junction, which causes the voltage to be a non-linear function of charge stored in the junction. The outstanding promise of charge coupled devices is in the enormous signal processing capability which is available when signals are converted to charge packets which may be processed very efficiently. However, if the input signal is converted with non-linear distortion into charge, the error associated with complex linear signal processing of non-linear charge cannot be recovered. Many varied circuits have been developed to provide an effective linearization at the input of charge coupled devices, as discussed below. At the output of such charge coupled devices, however, only the most complicated charge amplifier configurations provide acceptable linearity for most signal processing applications. These techniques reduce yield, increase power consumption and add substantial noise at the output, which limits performance. An order of magnitude improvement is needed without disadvantages of the current linearization techniques. Significant effort has been invested by the semiconductor industry toward this end. Specifically, a technique discussed in M. F. Tompsett, "Surface Potential Equilibration Method of Setting Charge in Charge Coupled Devices," IEEE Transactions on Electron Devices, Vol. ED-22, No. 6, June 1975, p. 305, overcame the thermal and voltage sensitivities of early charge coupled device diffusion input techniques. This technique includes non-linearities associated with depletion capacitance if a differential input is required.
Other techniques have been proposed to provide linearity between the input and the output of a charge coupled device. For example, D. J. MacLennan, "Linearization of the Charge Coupled Device Transfer Function," 1975 Proceedings of the International Conference on the Application of Charge Coupled Devices, p. 291, October 1975, discloses an operational amplifier at the charge coupled device input with feedback from an input floating gate. The techniques disclosed in R. W. Broderson, et al., "A 500-State CCD Transversal Filter for Spectral Analysis," IEEE Transactions on Electron Devices, Vol. ED-23, pp. 143-152, 1976 and C. H. Sequin, et al., "Self-Contained Charge Coupled Split-Electrode Filters Using a Novel Sensing Technique", IEEE Journal of Solid-State Circuits, SC-12, p. 626, December 1977, both involve a voltage signal applied to the input diffusion of a charge coupled device, but require output feedback to the sense electrode at a fixed potential. Such output feedback usually adds noise to the output signal and requires complex circuitry. The method disclosed in Y. A. Haque and M. A. Copeland, "Design and Characterization of a Real-Time Correlator," IEEE Journal of Solid-State Circuits, Vol. SC-12, p. 642, December, 1977, uses the voltage input technique of the Broaderson publication, but does not have a perfectly linear output. Finally, the technique discussed in C. R. Hewes, "A Self-Contained 800 Stage CCD Transversal Filter," Proceedings of the 1975 International Conference on the Application of Charge Coupled Devices, p. 309. October, 1975, employs a diffusion input scheme in a charge coupled device to compensate output non-linearities, which makes the intermediate signal processing non-linear. Thus, the prior art has used charge injection and charge sensing techniques which involve a non-linear relationship between charge and voltage because the device capacitance is not constant.